Pediatric obstructive sleep apnea (OSA) is a prevalent disorder, with a high burden among minority children. There is growing evidence that when untreated, it is associated with numerous adverse health outcomes, including neurocognitive and behavioral deficits, impaired quality of life, and cardiovascular and metabolic sequelae. The first line treatment is adenotonsillectomy (AT), which is the second most common pediatric operation, accounting for $500 million of annual health care costs. Despite the prevalence of OSA, its broad range of co-morbidity, and the frequency of surgical treatments, there has not been a single rigorously controlled trial that has addressed either the efficacy of the procedure or potential differences in treatment responses among vulnerable groups such as overweight children and ethnic minorities. To address this critical gap, we have assembled a group of expert centers in pediatric OSA, with a range of sleep medicine, otolaryngology, neurobehavioral, epidemiological, and biostatistical expertise to address the hypothesis that AT for treatment of OSA in children aged 5 to 9 years will result in improvements in health outcomes determined 6 months following AT. Over a 2.5 year recruitment period, we will enroll 460 children (50% minorities) with OSA from the otolaryngology and sleep referral clinics of four clinical sites (Children's Hospital of Philadelphia, Cinncinatti Children's Hospital, Kosair Children's Hospital, Rainbow Babies and Children's Hospital), randomizing 50% to early AT and 50% to deferred surgery (with treatment decisions reevaluated after a 7 month observation period). At baseline and 7 months later, we will obtain standardized overnight polysomnography, morning and evening blood pressures, anthropometry, a fasting blood sample, and perform a comprehensive assessment of neurocognitive and behavioral functions. Selected clinical endpoints also will be re-evaluated at 12 months. Quality assurance for polysomnography, surgery, and neurobehavioral measurements will be directed by centralized cores at Case School of Medicine and the University of Michigan. Analyses will address whether AT is associated with improvement in attention and neurocognitive executive functions and sleep-related breathing disturbances, and whether changes in indices of OSA correlate with changes in other outcomes. Secondary analyses will address treatment effects on learning/memory, behavior, quality of life, growth, blood pressure, and biochemical indices of insulin resistance and inflammation. These will be the first data from a randomized controlled study, with geographic and ethnic representation, to address treatment efficacy for a common pediatric condition and to identify sub-groups, such as overweight children, with potential differential treatment responses. These data will be critical for defining treatment indications for a common surgical procedure, for identifying subgroups who require more intensive monitoring, and for understanding the co-morbidity of OSA.